Positive displacement metering apparatus

ABSTRACT

This apparatus provides positive displacement synchronized metering of pressurized food material to a plurality of dies using several positive displacement metering apparatus. The metering is provided by the energy of pressurized material itself, or, for more viscous material, it can be supplemented by a motor. Supplemental material can also be introduced along with the food material to modify the characteristics of the food material.

This is a continuation application of pending prior U.S. applicationSer. No. 08/452,114, filed on May 26, 1995, now U.S. Pat. No. 5,536,517.

FIELD OF THE INVENTION

The present invention relates to metering viscous food material to aplurality of extrusion dies. More specifically, this invention teachesthe use of positive displacement metering to a plurality of extrusiondies.

BACKGROUND OF THE INVENTION

A number of food extrusion processes require an equal flow of materialfrom a number of dies which are fed from the same die holder. If theflow of material is unequal then the resulting product streams are alsonon-uniform which is undesirable.

This is particularly true if the food material is cut to a predeterminedlength with an estimated weight for packaging based upon the length,which is not unusual in extruded food packaging.

A number of arrangements have been provided to attempt to provide equalamounts of food material from a number of dies with each die extrudingthe same quantity per unit time. Previous attempts have been directed toproducing the same pressure on each die in an attempt to obtain the samequantity of extruded product per unit time.

A example of the prior art, before an attempt was made to obtain equalpressure on each die, is shown in FIG. 1. Here extrusion apparatus 12has a source of heated material introduced through pipe 32 into amanifold 26, which can be heated. Dies 18 are all connected to dieholder 20, which has a conduit 21 opposite each die from die holder 20into manifold 26. The result of this arrangement is shown in FIG. 1Awith the resulting pressure in pounds per square inch (PSI) as afunction of die location 13. FIG. 1A is also positioned opposite FIG. 1such that the die locations of FIG. 1A all directly relate to the die 18locations of FIG. 1. Since pipe 32 is centrally located the maximumpressure is also centrally located with a reduction in this pressureoutwardly in both directions as shown in FIG. 1A.

An attempt to remedy this,situation is shown in FIG. 2 where extrusionapparatus 14 has two pipes 34 feeding heated pressurized food materialinto manifold 28. Conduits 23 extend between manifold 28 to die holder22 opposite each die 18. The results of this arrangement is shown inFIG. 2A with the resulting pressure in pounds per square inch (PSI)plotted as a function of die location 15. FIG. 2A is also positionedopposite FIG. 2 such that die 18 locations of FIG. 2A correspond to thedie locations of FIG. 2. Since pipes 34 are spaced approximatelyone-third of the distance along manifold 28, two maximums essentiallyopposite pipes 34 occur, with a reduction in these pressures outwardlyin both directions as shown in FIG. 2A. This is an improvement over theresults of extrusion apparatus 12 but the pressure of each die is stillfar from equal.

An improved attempt to provide equal pressure on dies 18 is shown inFIG. 3 with extrusion apparatus 16 again having only one pipe 36 feedingheated pressurized food material into manifold 30. Conduits 25 extendbetween manifold 30 to die holder 24 opposite each die 18. Here howevereach die 18 has a valve 38 in connection 23 to die holder 24. Valves 38permit adjusting the pressure on each die 18 independently. The resultsof this arrangement is shown in FIG. 3A with the resulting pressure inpounds per square inch (PSI) plotted as a function of die location 17.FIG. 3A is also positioned opposite FIG. 3 such that die 18 locations ofFIG. 3A correspond to the die locations of FIG. 3. Here the resultingpressure is nearly equal at all dies because valves 38 have beenadjusted to achieve this result.

Even extrusion apparatus 16 does not produce the desired result of auniform quantity of material extruded from each die 18 over any giventime period. This results because the quantity being adjusted, namelypressure, is not the quantity which must be kept uniform, namelyextruded material per unit time. Equal pressure on dies 18 will onlyproduce equal flow if the material friction to and through each dieremains identical, and if the material being extruded through each diehas identical viscosities. Any difference in the temperature of a foodmaterial will result in a change in its viscosity, with lowertemperatures resulting in greater viscosity. Dies 18 located at the endsof die holder 24 will receive material which has a longer flow path witha greater length of time to cool with a resulting greater viscosity,which will cause some of to adhere to the die intake reducing its sizeand increasing its friction. While a small differential is insignificantinitially, the effects build up exponentially with time. Consequently, asmall reduction in flow caused by lower temperature causing greaterviscosity will result in the material being fed to that die flowing evenslower, which increases the temperature differential even further. Thisbuilds up into a catastrophic failure quickly until the die is blockedcompletely. This is an inevitable result of any temperature differentialin the material, and will always result in die blockage. Once even onedie is blocked the die assembly must be disassembled and cleaned beforeit can be used further. These problems are multiplied when extrudingmultiple phases at one time, or when the material contains lumps ofmaterial of a size which can plug a die.

Meisner, in U.S. Pat. No. 4,925,380 and 5,019,404 utilizes a scheme formanufacturing a multicolored aerated confection product utilizingmulti-orifice extrusion system for extruding multiple strands of aconfection material. These apparatus have the problems discussed abovesince no provision is made for metering equal amounts of materialthrough individual dies.

A number of apparatus utilize positive displacement metering of bothplastic and food materials to extrusion apparatus obtain a uniformproduct. These include Fox, U.S. Pat. No. 4,336,213; Rahlfs, U.S. Pat.No. 4,171,193; Fritsch, U.S. Pat. No. 3,649,147; R. Levison et al., U.S.Pat. No. 3,078,513; H. Corbett, U.S. Pat. No. 2,680,880; and Marin, U.S.Pat. No. 5,182,066

All of these positive displacement metering apparatus drive only asingle extrusion die. There is no teaching of using a number ofsynchronized positive metering apparatus to provide a plurality ofuniform and equal extrusions.

This invention positively meters food material through a plurality ofdies. This assures that all flows remain open to all dies and ratepredetermined by the capacity of the various metering means. This resultis obtained regardless of the temperature of the material flow to anygiven die and completely overcomes the problems of all previousextrusion apparatus to multiple dies, where even a small temperaturedifferential will always cause the catastrophic failure of total dieblockages.

In the prior art using pressure balancing to obtain uniform flow throughmultiple dies, the flow rates are dependent upon the sum of all pressurelosses along all flow paths including the flow path through each die.This invention frees the die designer from the constraint of balancingthe pressure losses in each flow path to the individual dies. This cangreatly simplify the die design itself, which results in a die easier tomanufacture and clean. As an alternative, a more complex die can now beused to obtain previously unattainable results.

SUMMARY OF THE INVENTION

This invention provides several embodiments of apparatus for extrudingstreams of food material through a plurality of dies using severalmetering means to prevent blockage of any individual die caused bymaterial temperature differentials, and procedures for doing the same.In one embodiment a manifold, which provides a source of heatedpressurized food material, feeds a plurality of pairs of gears havingintermeshed portions which meter the material. These intermeshedportions of the gear pairs interposed between the manifold and each diethe intermeshed portion of each gear pair having an input receivingmaterial from the manifold and an output feeding a separate die.Typically the gear pairs will all have identical displacements, howeversome pairs of gears can have different displacements by such means ashaving a different width or tooth depth to produce a differentdisplacement, if desired.

The gears are arranged such that a first half of the gears has a firstshaft extending through them and a second half has a second shaftextending through them, with the first shaft having all the gears itextends through affixed to the shaft and the second shaft free-wheeling.This attachment of the first shaft forces all the gear pairs to rotatetogether in synchronism. This ensures that material will be metered by agear pair through each die regardless of temperature differentials inthe material creating differences in the material consistency. Thisresults because the pressurized material introduced into the input ductacts upon all the intermeshed portions of all gear pairs and providesenough energy to them to cause them to rotate. All gears rotate insynchronism because of the first shaft attachment, and any localadditional stiffness of material adjacent to any gear pair will not stopthe rotation of the shaft. Since the rotation of the shaft rotates allgear pairs and the gear pairs provide positive displacement metering,material will continue to be fed to all dies regardless of localizedviscosity changes.

The gear pairs provide a metering function only, the pressure of thematerial leaving each gear pair being less than the pressure of thematerial entering each gear pair. The pressurized material need onlyprovide enough energy for metering and need not provide enough energyfor pumping. Further, the spacing between the gears in the gear pairsmust be quite large for metering which is incompatible with pumping. Anyfood material with a cP of 100,000 or less can be metered by the energyfrom the pressurized food material alone. This includes marshmallow foodwhich has a cP of around 100,000. A cp of around 100,000 results in apressure drop of approximately 100 psi across a gear pair.

If all the gear pairs have identical displacements the material streaminto each die will be equal because of the shaft interconnection. If thegear pairs are unequal in displacement the material streams will also beunequal, but will have a volumetric ratio directly proportional to thegear pair displacements.

Some food material is too viscous for the food pressure to provideadequate energy to operate the gear pairs in the manner described, sincefood material can have a cP of up to 20,000,000. As an example, usingthis arrangement material with a 1,000,000 cP would result in a pressuredrop of greater than 150 psi. This is an unacceptably large pressuredrop and would result in product shear damage. In addition, the largetolerances between the gears required for metering would permit foodmaterial to leak around the gears rather than turn them. These problemsare overcome in a variation to this embodiment by having the shaftdriven by a motor to provide additional energy. This driven arrangementhas a maximum operating cP range of up to 20,000,000. Here again thepressurized material energy and motor energy,need only be adequate formetering and not for pumping.

The motor driving the common shaft can be provided with a controller.This controller can cause the motor to drive the shaft at a uniformrotation rate, resulting in uniform extrusions from each die with theratio between them being determined by the gear pair displacements asbefore, or the controller can have selectable means to cause the shaftto rotate at varying predetermined rotation rates for special effects.This can including stopping the shaft for a predetermined period of timeor even pulsing the shaft intermittently. Appropriate apparatus toobtain varying rotation rates can be accomplished by a number ofmechanical or electrical apparatus and can readily be selected by thoseskilled in the art.

Each gear pair meters the material and as a side effect also mixes itvery well. This results because the gears meshing shears material caughtin the teeth to provide an effective mixing action. This mixing actioncan be used to advantage by introducing an extrudable or even a pumpablesupplemental material, under pressure which is substantially the same asthat of the pressurized food material, into a gear pair input where thegear pair will mix it with the food material. This extrudablesupplemental material can include such things as a liquid, a viscoussolid, or a combination thereof. These examples are given asillustrations and not as a limitation, any material which can be pumpedor extruded can be used as a supplemental material.

This supplemental material can itself be or can contain a coloringagent, a flavoring agent, or any other agent or combination thereofwhich will modify a characteristic of the food material. Injectedsupplemental material which is a liquid will be mixed well with the foodmaterial by the action of the gear pair itself with no additionalequipment being required. For extrudable material, static mixers, whichare well known in the art, can be placed in the material stream betweenthe meter and the die. This permits doing such things as extrudingstreams of food from different dies having different colors or flavorswhile using only one food material.

The supplemental material can itself be displacement metered. When gearsare used for metering, the gears of the supplemental material gear paircan be attached to the same shafts as the other gear pairs with itsoutput flowing into the input of the gear pair metering the foodmaterial. Since this is supplemental material a smaller volumetric flowis required than that of the food material, but since the volumetricdisplacements of the two gear pairs can be made different as describedearlier, this is a feasible requirement.

Other embodiments to the invention use different positive displacementmetering of lobe impellers with either one or two lobes opposed to eachother on two shafts as in the gear pairs. Here too the energy formetering can be provided by the energy of the pressurized material orthe energy can be supplemented by a motor. When lobe impellers are usedthe arrangement is almost identical to the gear pump arrangement where aplurality of lobe pumps feed a plurality of dies. Here however, the twoshafts must both be attached to the opposed lobe pairs and the shaftsmust be synchronized by a gear pair since opposed lobe impellers are notself synchronizing.

Another embodiment uses a plurality of vane impellers on a single shaftfor metering food material to a plurality of dies. Here too the energycan be provided by the pressure of the material or the energy can alsobe supplemented by a motor.

These apparatus and methods of using the same provides simple andeffective means to completely overcome the previous problem of foodmaterial temperature differentials resulting in the catastrophic failureof a build-up of material completely blocking a die, because of thepositive displacement action of the metering means. All of the meteringmeans embodiments are arranged to be mounted in a split housing which issimply unbolted to remove and clean the metering apparatus. Thesimplicity of this apparatus is important because all equipment used forfoodstuffs must be kept scrupulously clean. Cleaning complex machineryto the level required for foodstuffs is extremely difficult. Theprevious catastrophic build-up of food materials completely blocking thedies also required disassembly and cleaning every time a die was blockedwith sanitation problems resulting from this repeated disassembly.

In addition to the various positive displacement metering meansprovided, this apparatus and method provides the capability of extrudingstreams of material having different colors and/or flavors from a singlefood material.

DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, and 3 show pertinent prior art at successive stages ofdevelopment.

FIGS. 1A, 2, and 3A show the resulting pressure curves versus dieposition for successive stages of prior art development.

FIG. 4 shows an isometric view of the mechanical elements of the instantinvention with the supporting apparatus being shown schematically.

FIG. 5 shows an exploded view of the mechanical elements of the instantinvention.

FIG. 6 shows a cross-section of FIG. 4 taken along 6--6.

FIG. 6A shows a cross-section of FIG. 6 taken along 6--6.

FIG. 7 shows a spacer between gear pairs.

FIG. 8 shows a two lobe positive displacement metering with shafts andsynchronizing gears shown schematically.

FIG. 9 shows a three lobe positive displacement metering with shafts andsynchronizing gears shown schematically.

FIG. 10 shows vane displacement metering.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An overview of multidie extrusion apparatus 50 is shown in FIG. 4. Ahopper 52 with counter-rotating augers 54 mounted along the bottom whichare driven by motor 56, force food material placed in the hopperrightward through pipe 58 and into pump 60. Pump 60 is driven by motor62. Pump 60 pressurizes the material and forces it into heater 66through pipe 68. A pressure sensor 127, mounted on the end of manifold70, senses the internal pressure for feedback to motor 62 to obtainconstant pressure on the material pumped into pipe 68. A heater andthermostat, not shown, heats the material within manifold 70 to apredetermined thermostatically controlled temperature.

The heated pressurized material flows from heater 66 into manifold 70through pipe 68. Manifold 70 is adjacent to divided metering housing 73.Material 78 which was transported from manifold 70 through meteringhousing 73 thence to a number of dies 74, not shown in this figurelocated within die housing 76, is extruded as streams of such materialto conveyor 80, where they are carried away. This paths for the flow ofmaterial will be described later.

Manifold 70, divided metering housing 73, die housing 76 and die holder86 are also shown in FIG. 5. Eight bolts 77 with attached nuts, notshown in this figure, extend through four upper holes 82 and four lowerholes 84 in these parts hold them all together.

Metering housing 73 is made up of an input portion 88 and an outputportion 90 which are essentially mirror images of each other. A set ofseven holes 92 which are aligned with each other provide a path for foodmaterial from manifold 70 through input housing portion 88. One hole isomitted because supplemental material rather than food material is fedto the metering means through a different hole, as will be describedlater. A second set of eight input duct holes 94 in input housingportion 88, aligned with holes 92, provide a path for food materialthrough input housing portion 90. A third set of eight output duct holes95 aligned with holes 94 provide a path to die housing 76. Dies 122, asshown in FIG. 6A, receive and extrude streams of material 78, shown inFIG. 4, received from output duct holes 95.

A shaft 96 extends through and is affixed to eight upper gears 98 and alower shaft 100 extends through and is free-wheeling to eight lowergears 102. Each of the eight upper gears 98 are intermeshed with anopposite lower gear 102. This intermeshing of an upper gear 98 with alower gear 102 provides a positive displacement metering function. Inputduct holes 94 in input portion 88 and output duct holes 95 in outputportion 90 of metering housing 73 are aligned with opposed intermeshedportions of gears 98 and 102 which respectively receive and exhaustmetered material. Each end 106 of gear frame 104 rotatably holds shafts96 and 100. Spacers 105 of gear frame 104, located between each opposedpair of gears 98 and 102 also shown in FIG. 7, are shaped to closely fitwithin the cavity formed by recess 108 in input portion 88 and recess110 in output portion 90 of metering housing 73. Gaskets 112 mountedaround each spacer 105 seal material within each gear pair. In addition,bearings and seals mounted within each seal on each spacer 105 aroundshafts 96 and 100, not shown, seal the shafts and permit the shafts torotate.

FIG. 6 shows metering housing 73, made up of input portion 88 and outputportion 90, and die housing 76, all being held together by bolts 77 andattached nuts 79. An upper gear 98 is shown intermeshed with a lowergear 102, with input duct hole 94 opposite output duct hole 95 and bothopposite the intermeshed portion of the gears. Die 74 communicates withoutput duct hole 95 to receive material from the metering gears. Uppershaft 96 through upper gear 98 and lower shaft 100 through lower gear102 can be seen. FIG. 6A shows die opening 122 of one of the dies 76which extrudes material. As also shown in FIG. 4, hole 114 extendsthrough input housing portion 88 into the outermost input duct hole 92with pipe 116 conveying pressurized supplemental material frompressurized tank 117 into the hole. Pipe 116 injects supplementalmaterial into the gear pair adjacent to frame end 106 to be mixed withfood material.

As shown in FIGS. 4 and 5, hole 118 through input housing portion intothe input duct hole 94 second from end 106 has a pipe 120 conveyingsupplemental material into this hole from pressurized tank 117. Thisinjects supplemental material only into the second pair of gear pairs tobe metered, since the opposed manifold hole 92 is blocked hole 122opposite output duct hole 95 provides this metered supplemental materialto pipe 124 to be conveyed to hole 126 into the adjacent inner inputduct hole 94, which is third from outer end 106, to be mixed with foodmaterial from opposite input duct hole 94.

Streams of material 78 are shown being extruded from dies 122 onto amoving conveyor belt 80 arranged to carry the extruded material awayfrom all gear pairs, excepting only the second gear pair from the outerend as explained earlier.

Motor 128 is connected to and drives upper shaft 96 in a direction whichwill meter material from input duct holes 94 through metering gears 98and 102 through output duct holes 95. Motor controller 130 will causeshaft 96 to rotate at a constant speed unless modified by selectablecontrol apparatus 132 which will cause the shaft to rotate at one of anumber of preselected variable rates which change with time. Motorcontroller 130 can be any one of a number of available motor controllersknown in the art. In addition, control apparatus 132 providing a numberof selectable variable changing rotation rates can be mechanical,electrical, computer generated or a combination thereof.

Apparatus such as this is currently available in all these forms and oneskilled in the art can readily select an appropriate control apparatusfor this application.

The positive displacement metering means described above is not the onlypositive displacement apparatus which can be used. FIG. 8 shows two lobepositive metering apparatus 136 comprised of opposed two lobe impellers138 and 140 affixed to shafts 142 and 144 respectively, which interleaveto provide positive displacement metering. Shaft 142 replaces shaft 99and shaft 144 replaces shaft 100 in FIG. 4, with housing 73 modifiedappropriately to contain eight two lobe positive displacement meteringapparatus 136 in the same manner as the opposed upper gears 98 and lowergears 102. Synchronizing gears 99 and 101 are mounted on the end ofshafts 142 and 144 respectively with both shafts affixed to therespective two lobe impellers 138 and 140, because the two lobeimpellers are not self-synchronizing.

Shaft 142 can be driven by the pressurized material itself actingagainst the interleaved two lobe impellers 138 and 140, or it can bedriven by motor 128, which can also be controlled as before for constantor varying rotation rates.

FIG. 9 shows three lobe positive displacement metering apparatus 150,comprised of three lobe impellers 152 and 154 affixed to shafts 156 and158 respectively, which interleave to provide positive displacementmetering. Shaft 156 replaces shaft 99 and shaft 158 replaces shaft 100in FIG. 4, with housing 73 modified appropriately to contain eight threelobe positive displacement metering apparatus 150 in the same manner asthe opposed upper gears 98 and lower gears 102. Here synchronizing gears160 and 162 are again mounted on the end of shafts 156 and 158respectively with both shafts affixed to the respective three lobeimpellers 152 and 154, because the three lobe impellers are also notself synchronizing. Shaft 156 can be driven by the pressurized materialacting against three lobe impellers 152 and 154 or it can be driven bymotor 128, which can also be controlled as before for constant orvarying rotation rates.

Another positive displacement metering means is shown in FIG. 10 wherepositive displacement vane metering apparatus 166, mounted on shaft 170,has vane impeller 166 having individual vanes which slideably mate withreceptacles and are urged outwardly therefrom by springs 168. Inlet 172and outlet 174 correspond to input duct holes 94 and output duct holes95 of metering housing 73, as shown in FIG. 5. Shaft 170 corresponds toupper shaft 96 of FIG. 6, however here only one shaft is used for thevane impellers. Housing 73 is modified appropriately to contain eightpositive displacement vane metering apparatus 166 in the same manner asthe opposed upper gears 98 and lower gears 102. Here synchronizing isnot required because of only one shaft being used.

Shaft 170 can be driven by the pressure of the material against the vaneimpellers 166, or it can be driven by motor 128, which can also becontrolled as before for constant or varying rotation rates.

This simple mechanical apparatus, which is easy to disassembly andclean, will extrude multiple streams of material with predetermined flowrates, depending upon the capacity of the gear pumps, with nopossibility of unequal temperatures within the material mix causing anyblockage of dies. In addition to continuous flow rates, non-uniform flowrates can be selected. Having the metering means arranged for easycleaning is imperative in machinery for foodstuffs. Further,supplemental material can either be injected or metered into the foodmaterial at the input to the metering gears to provide extruded streamshaving different characteristics, such as color or flavor, using only asingle food material.

While this invention has been described with respect to a specificembodiment, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiment, aswell as other embodiments of the invention, will be apparent to personsskilled in the art upon reference to this description. It is thereforecontemplated that the appended claims will cover any such modificationsor embodiments as fall within the true scope of the invention.

I claim:
 1. Apparatus for metering pressurized, viscous food materialcomprising:a plurality of positive displacement metering means havinginput means for receiving material to be metered and output means fordischarging metered material, said metering means being operated withenergy obtained from said pressurized material; and meansinterconnecting a predetermined number of said metering means forsynchronizing the interconnected ones of said metering means.
 2. Theapparatus of claim 1, further comprising means for supplementing theoperating energy provided by said pressurized material.
 3. The apparatusof claim 1, further comprising supplementary operating energy means formaintaining pressure at said output means approximately equal to thepressure at said input means.
 4. The apparatus of claim 3, wherein saidsupplementary operating energy means comprises control means formetering uniform quantities of material as a function of time.
 5. Theapparatus of claim 4, wherein said control means comprises means forselecting one of a plurality of different predetermined non-uniformquantities of material for metering as a function of time.
 6. Theapparatus of claim 1, further comprising means for controlling thequantity of pressurized material metered by said metering means as afunction of time.
 7. The apparatus of claim 1, wherein said input meanscomprise duct means and further comprising means for introducingpressurized supplemental material into the input duct means of at leastone metering means.
 8. The apparatus of claim 7, further comprisingsecond positive displacement metering means for metering saidsupplemental material.
 9. The apparatus of claim 8, wherein saidinterconnecting means synchronizes said second metering means with saidplurality of metering means.
 10. The apparatus of claim 7, wherein saidoutput means comprise duct means and wherein said supplemental materialintroducting means comprises means interconnecting the output duct meansof at least one metering means with the input duct means of anothermetering means.
 11. The apparatus of claim 1, wherein:individual ones ofsaid metering means comprise an intermeshed portion of a first gear anda second gear of a gear pair, said individual ones of said meteringmeans further comprising a first shaft and a second shaft, said firstshaft extending through said first gears, and said second shaftextending through said second gears; said gear pairs having a supportingenclosure therearound arranged such that said gear pairs and shafts canrotate freely therewithin with all shafts and all gear pairs beingsealed from the outside and from each other; said interconnecting meanscomprising attachment of said first gears to said first shaft.
 12. Theapparatus of claim 11, further comprising motor means for providingadditional energy for driving said first shaft in a rotation directionsuch that material for each gear pair is metered from said input meansto said output means.
 13. The apparatus of claim 12, wherein said motormeans includes speed control means for metering uniform quantities ofmaterial as a function of time.
 14. The apparatus of claim 13, whereinsaid control means comprises means for selecting one of a plurality ofdifferent predetermined non-uniform quantities of material for meteringas a function of time.
 15. The apparatus of claim 1, wherein:individualones of said metering means comprise opposed multilobed interleavedidentical first and second impeller means for metering material, saidindividual ones of said metering means further comprising a first shaftand a second shaft, and a first synchronizing gear and a secondsynchronizing gear, said synchronizing gears being mated and engagingeach other, said first shaft extending through and being affixed to allfirst impellers and said first synchronizing gear, and said second shaftextending through and being affixed to all second impellers and saidsecond synchronizing gear, all said impellers having a supportingenclosure therearound arranged such that said impellers and shafts canrotate freely therewithin with all shafts and all impeller pairs beingsealed from the outside and from each other.
 16. The apparatus of claim15, wherein said first and second impellers each comprise two lobes. 17.The apparatus of claim 15, wherein said first and second impellers eachcomprise three lobes.
 18. The apparatus of claim 1, wherein:individualones of said metering means comprises a plurality of positivedisplacement vane metering means comprised of vane impellers formetering material, said individual ones of said metering means furthercomprising a shaft, said shaft extending through and being affixed toall vane impellers, all said vane impellers having a supportingenclosure therearound arranged such that said impellers and shaft canrotate freely therewithin with said shafts and said impellers beingsealed from the outside and from each other.